Does carbon monoxide treatment alter cytokine levels after endotoxin infusion in pigs? A randomized controlled study
Journal of Inflammation
Does carbon monoxide treatment alter cytokine levels after endotoxin infusion in pigs? A randomized controlled study
Anna-Maja berg 0
Pernilla Abrahamsson 0
Gran Johansson 0
Michael Haney 0
Ola Wins 0
Jan Erik Larsson 0
0 Address: Division of Anaesthesiology and Intensive Care Medicine, Department of Surgical and Perioperative Sciences, Umea University Hospital , Umea , Sweden
Background: Carbon monoxide (CO) has recently been suggested to have anti-inflammatory properties, but data seem to be contradictory and species-specific. Thus, in studies on macrophages and mice, pretreatment with CO attenuated the inflammatory response after endotoxin exposure. On the other hand, human studies showed no effect of CO on the inflammatory response. Antiinflammatory efficacy of CO has been shown at concentrations above 10% carboxyhaemoglobin. This study was undertaken to elucidate the possible anti-inflammatory effects of CO at lower CO concentrations. Methods: Effects of CO administration on cytokine (TNF-alpha, IL-6, IL-1beta and IL-10) release were investigated in a porcine model in which a systemic inflammatory response syndrome was induced by endotoxin infusion. Endotoxin was infused in 20 anaesthetized and normoventilated pigs. Ten animals were targeted with inhaled CO to maintain 5% COHb, and 10 animals were controls. Results: In the control group, mean pulmonary artery pressure increased from a baseline value of 17 mmHg (mean, n = 10) to 42 mmHg (mean, n = 10) following 1 hour of endotoxin infusion. Similar mean pulmonary artery pressure values were found in animals exposed to carbon monoxide. Plasma levels of all of the measured cytokines increased in response to the endotoxin infusion. The largest increase was observed in TNF-alpha, which peaked after 1.5 hours at 9398 pg/ml in the control group and at 13395 pg/ml in the carbon monoxide-exposed group. A similar peak was found for IL-10 while the IL-6 concentration was maximal after 2.5 hours. IL-1beta concentrations increased continuously during the experiment. There were no significant differences between carbon monoxide-exposed animals and controls in any of the measured cytokines. Conclusion: Our conclusion is that 5% COHb does not modify the cytokine response following endotoxin infusion in pigs.
Carbon monoxide (CO) is recognized as a toxic gas in
humans, originating from tobacco smoke, car exhaust and
fire. CO bound to haemoglobin (Hb) can lead to injury
related to impaired oxygen delivery, since the affinity of
Hb for CO is much greater than for oxygen. CO also
interferes with cellular respiration through the electron
transport chain by inhibition of cytochrome c oxidase.
However, some studies suggest that CO also has positive
biological effects such as a vasodilative action [1,2]. Many
in vitro studies, as well as studies in rodents postulate
anti-inflammatory effects of CO [3-7]. A conflicting lack
of effect of CO was found in humans after endotoxin
exposure, where no protective or anti-inflammatory
effects were demonstrated .
Our hypothesis was that a low dose of CO has protective
anti-inflammatory effects during sepsis. We aimed to test
this using a model of endotoxin-induced systemic
inflammation in pigs. Further, we aimed to test this at CO levels
below concentrations that may be toxic.
The study was approved by the Animal Experimental
Ethics Committee and performed in accordance with the NIH
Institutional animal care and use committee guidebook. A
total of 20 female pigs weighing 2340 kg were used. They
were delivered from the breeder to the University stable
and kept overnight.
For premedicination, a mixture of ketamine 10 mg/kg
(Ketalar, Pfizer, Morris Plains, New Jersey, USA),
azaperone 4 mg/kg (Stresnil, Janssen-Cilag, Neuss, Germany)
and atropine sulphate 0.05 mg/kg (Atropin, NM Pharma,
Stockholm, Sweden) was given intramuscularly.
Anaesthesia was induced by an intravenous bolus dose of 10
mg/kg sodium pentobarbital (Pentobarbitalnatrium,
Apoteksbolaget, Stockholm, Sweden). Infusion of
fentanyl (Fentanyl, Braun, Melsungen, Germany) 20 g/kg/h,
midazolam (Dormicum, Roche, Basel, Switzerland) 0.3
mg/kg/h and sodium pentobarbital 5 mg/kg/h was used
for maintenance of anaesthesia. The animals were
tracheotomized (7.0 OP endotracheal tube, Rusch, Kernen,
Germany) and mechanically ventilated with air containing
30% oxygen (Evita 4, Drger, Germany). The ventilator
was set to give a positive end-expiratory pressure of 3 cm
H2O. Ventilation was adjusted to obtain
normoventilation, as determined by the goal of PaCO2 levels between
4.5 and 5.5 kPa, as measured with intermittent arterial
blood gas analyses (ABL5 autoanalyzer, Radiometer,
Copenhagen, Denmark). During the protocol, the
fraction of inspired oxygen (FiO2) was adjusted to avoid
hypoxia (FiO2 varied between 30100%), as measured by
the arterial oxygen saturation (SaO2) of haemoglobin and
the Hb concentration (OSM3 hemoximeter, Radiometer,
Denmark). A SaO2 of more than 90% and a Hb
concentration of more than 90 g/l were considered sufficient for this
purpose. One litre of Ringer's acetate was given to the
animals during the first hour of the preparation and
stabilisation period, and was followed by an infusion that started
at 15 ml/kg/h and was increased during the day to
maintain normovolemia, as determined by the goal to achieve
a CVP between 5 and 10 mmHg.
All vascular catheterisations were conducted by vessel
cutdowns in the neck. An arterial catheter was placed in a
small neck artery. A central venous catheter was inserted
in the external jugular vein. A 7F, 4-lumen,
balloontipped pulmonary artery catheter (Optimetrix, Abbot Inc.
Illinois, USA) was placed to an occlusion position in the
pulmonary vascular tree, where the balloon was deflated
and the catheter secured. Measurements included heart
rate (HR), mean arterial pressure (MAP), central venous
pressure (CVP) and mean pulmonary arterial pressure
(MPAP). Cardiac output was measured by thermodilution
with 5 ml iced saline as indicator (WTI, Wetenskappwlijk,
Technische Instituut, Rotterdam, The Netherlands). All
pressures were measured using fluid filled catheters and
pressure transducers (Ohmeda Inc., USA) at the
mid-axillary level. HR and all pressure measurements were
continuously recorded using a computer based multi-channel
signal acquisition and analysis system (Acqknowledge,
Biopac systems Inc., CA, USA).
The animals were randomized following pre-medication
to receive CO or not until equal numbers of CO-infused
and control pigs were obtained. The treatment was open
to all personnel performing the experiment. One hour
after the preparation, CO (5% in nitrogen) was
administrated to the low-pressure circuit of the ventilator. First, a
bolus of CO was given with the goal to obtain 5% COHb
in the blood, as determined by hemoxiometry (OSM3
hemoximeter, Radiometer, Denmark). This was followed
by delivery of CO at a flow rate of 450 ml/min
throughout the protocol to match a predicted clearance of 25 ml/
min  and to maintain a stable CO level, as measured by
COHb concentrations. Ten animals were used as controls
and were not given CO. Two hours after the preparation,
endotoxin (lipopolysaccharides from Escherichia coli,
0111:B4, Sigma, USA) was infused intravenously,
beginning at 0.05 g/kg/h and reaching 0.25 g/kg/h after 30
minutes, which was maintained during the remaining
protocol. This infusion rate aimed at a total dose of 1.175
g/kg to each animal. The endotoxin dose was not
adjusted when the animals demonstrated respiratory or
circulatory dysfunction. Blood samples were taken every
30 minutes. The total protocol time was 6 hours,
including 5 hours of endotoxin infusion.
A total of 13 blood samples were collected from each
animal. All arterial and mixed venous blood samples were
analysed immediately for PaO2, PaCO2 (ABL5 auto
analyzer, Radiometer, Denmark), Hb and Hb-saturation
(OSM3). Double samples of all 13 arterial blood samples
were collected in gas tight tubes and kept at 4C until they
were analysed for CO. CO analysis was performed using
gas chromatography (GC) with a nickel catalyst and flame
ionization detection (HP 5790A, Agilent Technologies
Sweden AB, Stockholm, Sweden), as described elsewhere
. The concentration from the gas chromatograph was
also calculated to COHb fraction using the
Where C is the CO concentration expressed in M, COHb
is the carboxyhaemoglobin fraction, Hb is the
haemoglobin concentration (g/l), 64400 is the molecular mass
of haemoglobin in mammals and the constant 4
represents the four binding sites of haemoglobin to carbon
Ten of the arterial blood samples were collected in EDTA
tubes (BD Vacutainer, NJ, USA) and centrifuged at 4C,
3000 G, for 20 minutes. The plasma was collected and
stored at -80C. These plasma samples were analysed for
cytokines (TNF-a, IL-6, IL-10 and IL-1beta) using ELISA
with porcine antibody kits (R&D Systems Inc., USA) in
accordance with the instructions delivered by the
manufacturer. The absorbance was read on a spectrophotometer
(Labsystems Multiskan MS, Triad Scientific Inc., USA).
A two-sample power analysis was performed using data
from an in vivo study in mice where the difference in
TNFalpha concentration between CO exposed animals and
controls was 30% in the group exposed to 10 ppm CO .
The standard deviation was calculated using SEM values
presented in the article and n = 7. Based on these results,
an experimental design with 10 animals in each group
would give a power of 99%, with an alfa p-level of 0.05
and a beta p-level of 0.007. For each measurement point
in each group, the one-sample Kolmogorov-Smirnov test
for normality was performed (SPSS 12.0, SPSS Inc.
Chicago, USA) for the parameters; MPAP, CO concentrations
and plasma cytokine concentrations. No significant
differences from normality were found at a p-level of 0.05,
indicating that these data were normally distributed. The
effect of CO on MPAP, plasma cytokine concentrations
and CO concentrations were analysed by SPSS 12.0 (SPSS
Inc., Chicago, USA) using mixed between-within subjects
analysis of variance for repeated measures (ANOVA). A
pvalue of less than 0.05 was considered to be a statistically
Seventeen of 20 animals completed the endotoxin
protocol and all measurement points. One animal in the CO
group died during the 4th hour of endotoxin infusion
resulting in missing values at 270 and 300 minutes. Two
animals from the control group died before the protocol
was completed, one after 2 hours of endotoxin infusion
and one after 3.5 hours of endotoxin infusion.
General circulatory and blood gas data
General circulatory and blood gas data from selected
measurement points are presented in Table 1. MPAP
increased to a first peak of almost 50 mmHg after 60
minutes of endotoxin infusion and reached a second peak at
approximately 180 minutes indicating a severe systemic
inflammatory response. There were no differences in this
pattern related to CO (Figure 1). Cardiac output decreased
during the protocol (Table 1). Levels of PaCO2 increased
iFMnideguauncreepdu1slmysotenmariyc ainrtflearmympraetisosnure in pigs after endotoxin
Mean pulmonary artery pressure in pigs after
endotoxin induced systemic inflammation. Values are
represented as means SEM for CO treated animals (open circles,
n = 10 except at 270 and 300 min where n = 9) and controls
(closed circles, n = 10 except at 150, 180 and 210 min where
n = 9 and at 240, 270 and 300 min where n = 8). Endotoxin
was administered (0.05 g/kg/h) just after time 0, reaching
maximum infusion rate (0.25 g/kg/h) at 30 min. CO was
administrated just after time -60 min. No significant
difference between the groups (ANOVA F(1, 9) = 0.158).
Administration of CO began 1 hour before the endotoxin infusion was started, whereas control animals received endotoxin infusion but no CO
inhalation. Values are presented as means SEM, n = 10 in each group (Control and CO), except otherwise stated (a, b, c; n = 9, 8, 7 respectively,
as indexed). Endotoxin was administered (0.05 g/kg/h) just after time 0, reaching maximum infusion rate (0.25 g/kg/h) at 30 min. CO was
administrated just after time -60 min.
during the experimental procedure, but remained within
the normocapnic range.
Results from blood analyses of CO concentrations are
presented in Figure 2, where 250 M corresponds to
approximately 5% COHb according to the transformation. The
control group showed very low CO concentrations
(approximately 50 M) with small inter individual
variability. CO administration to 10 animals resulted in steady
CO levels throughout the protocol, where 250 M in
blood was the target concentration.
Plasma cytokine measurements are shown in Figure 3.
TNF-alpha concentrations increased after 60 minutes of
endotoxin infusion and decreased after approximately
150 minutes. There was no difference between the groups
regarding TNF-alpha concentrations. There was a large
variation between individuals, especially at peak levels.
Two animals in the CO-treated group had much higher
TNF-alpha peak concentrations than the others.
Concentrations of IL-6 increased in response to endotoxin
infusion, with a peak at 150 minutes followed by a decrease,
but not to baseline levels. The two animals with extreme
TNF-alpha levels also had relatively high IL-6
concentrations. The individuals with the highest IL-6
concentrations were in the control group and died before the
protocol was completed. There was no statistically
significant difference in IL-6 concentrations between the groups.
The IL-10 concentration peaked at 90 minutes after which
it quickly decreased to near baseline levels and no
difference was observed between groups. IL-1beta increased
continuously during the protocol with the highest levels
after 5 hours of endotoxin infusion. One of the animals
with the highest IL-6 concentrations also had the highest
IL-1beta concentrations. This animal died before the
protocol was completed. IL-1beta concentrations were not
statistically significant different in CO-treated animals
compared with controls.
We were unable to show that administration of CO had
any effect on cytokine release during endotoxin-induced
inflammatory response. Pro-inflammatory cytokines
(TNF-alpha, IL-6 and IL-1beta) were neither attenuated in
CO-treated animals, nor did the anti-inflammatory
cytokine (IL-10) increase. These results were unexpected
and contrasted to findings in an endotoxin mouse model,
where lower TNF-alpha and IL-1beta and higher IL-10
levels in CO-treated animals compared with controls were
found . In the present study, 3 animals died before
completing the whole duration of the protocol, 2 control
animals and 1 animal in the CO exposed group. These
animals are not included in the statistical calculations due
to the limitations of ANOVA, resulting in the fact that the
animals that may have had the most powerful
inflammatory response may have been excluded from comparison.
Analysis of the data shows that the 3 animals that died
before completing the protocol did not have the highest
TNF-alpha or IL-10 concentrations. However, the highest
IL-1beta concentration was found in a control animal that
eFCniagdruobrotoenx2minoindouxcideed csoysntceemnticraitnifolanms minatthioentwinopgigrsoups after
Carbon monoxide concentrations in the two groups
after endotoxin induced systemic inflammation in
pigs. Values are represented as means SEM, for CO
treated animals (open circles, n = 10 except at 270 and 300
min where n = 9) and controls (closed circles, n = 10 except
at 150, 180 and 210 min where n = 9 and at 240, 270 and 300
min where n = 8). Endotoxin was administered (0.05 g/kg/h)
just after time 0, reaching maximum infusion rate (0.25 g/kg/
h) at 30 min. CO was administrated just after time -60 min.
died following 4 hours of endotoxin exposure. The 2
animals from the control group that died had the highest
IL6 concentrations. If these 3 animals would have survived
and been included the statistical analysis, this could imply
a difference in the interpretation of the IL-6 and IL-1beta
concentrations. However, these missing data do not have
any effect on the conclusion regarding TNF-alpha and
IL10 response which remains contradictory to the mouse
study . Published data on inflammatory effects of CO
in pigs is limited to only one other study, where higher
levels of TNF-alpha were found in CO-treated animals
compared with controls . It was concluded  that
although the TNF-alpha levels were higher in the CO
treated group, CO ameliorated several of the acute
pathological changes. They also found a suppression of IL-1beta
in the CO-treated group, resulting in a significantly higher
level of IL-1beta in the control group. This is in contrast to
our findings, which show no differences in IL-1beta
concentrations as a result of CO administration. One
explanation for this conflicting result could be that the other study
 only included 4 animals in each group. In a study in
man, where CO was administered before a bolus of
endotoxin was injected, there were no differences in plasma
cytokines (TNF-alpha, IL-6, IL-8, IL-10), cytokine mRNA
(IL-1 alpha, IL-1 beta), heart rate, MAP or SpO2 when the
CO-treated group was compared with controls . These
clinical findings also support the interpretation that CO
does not help to improve the inflammatory response after
endotoxin infusion. Our interpretation of previous
studies together with our findings is that CO may have an
antiinflammatory effect in mice but not in humans or pigs.
The cytokine levels following endotoxin infusion in our
study were high, and individual TNF-alpha levels were
found up to 46000 pg/ml. In comparison, other
endotoxin studies in pigs reported maximum levels of
TNFalpha of 3500 pg/ml , 4000 pg/ml , 9000 pg/ml
 or 20000 pg/ml , respectively. The cytokine
response for TNF-alpha, IL-6 and IL-10 following
endotoxin infusion shows the same pattern over time in our
study as has been observed by others , but the
IL1beta response was different. Our findings show an
increase in IL-1beta concentration during endotoxin
infusion, whereas the other study  showed no change in
In order to further evaluate possible anti-inflammatory
effects of CO, we have used a porcine model of human
sepsis. Pig sensitivity to endotoxin and tissue antigenicity
has been found to be similar to humans .
Furthermore, pigs also have similar cardiac anatomy and
physiology as humans . The endotoxin infusion model
appeared to provide a highly stable and predictable
circulatory and pathophysiological state for our study, as
demonstrated by a consistent biphasic MPAP pattern. The
endotoxin infusion rate was 0.25 g/kg/h, corresponding
to a total dose of 1.175 g/kg. The same dose has been
used in one other study investigating central
haemodynamics . This is a low dose compared with other pig
studies [11,13]. Since there are different serotypes of
endotoxin, there may be a wide range of potency.
Compared with other studies, which have employed the same
lipopolysaccharide serotype as in the present study
(0111:B4), we still have a low dose of endotoxin.
Endotoxin dosing regimens for the same serotype have been the
following; a bolus of 100 g/kg , a bolus of 75 g/kg
, and an infusion of a total dose of 250 g/kg .
Different batches of endotoxin probably have different
potency. Also, different breeds of pigs probably have
different sensitivity to endotoxin. The MPAP levels in our
study were high in comparison with other authors [11,20]
or similar . This acute increase in MPAP associated
with endotoxin administration (Figure 1) was close or
similar to levels found in cardiovascular decompensation.
Given this perspective of wide variation in endotoxin
dosing for pig sepsis models, our interpretation is that the low
endotoxin dose in our study resulted in large cytokine
release as well as high MPAP levels, indicating a massive
systemic inflammatory activation.
Mean CO inhalation
PFliagsumraec3ytokine concentrations in pigs after endotoxin-induced systemic inflammation with or without CO treatment
Plasma cytokine concentrations in pigs after endotoxin-induced systemic inflammation with or without CO
treatment. Values are presented as individual measurements for CO treated animals (open circles) and controls (closed
circles). A dotted (CO group) and solid (controls) line represents means for the two groups (n = 10 except for the CO-group at
270 and 300 min where n = 9 and for controls at 150, 180 and 210 min where n = 9 and at 240, 270 and 300 min where n = 8).
Endotoxin was administered (0.05 g/kg/h) just after time 0, reaching maximum infusion rate (0.25 g/kg/h) at 30 min. No
significant differences were detected between the groups for any of the cytokines (TNF: ANOVA F(1, 8) = 1.074, IL-6: ANOVA
F(1, 8) = 0.892, IL-10: ANOVA F(1, 8) = 1.347, IL-1beta: ANOVA F(1, 8) = 1.716).
The administration rate of CO in this study was chosen
with the aim to quickly achieve constant blood CO levels
and to avoid toxic effects. In contrast to a fixed CO dose,
the rate of delivery was modulated in order to maintain
relatively constant blood CO concentrations. An increase
in the CO administration rate was necessary during the
experiment, which we interpret as a result of reduced
pulmonary gas exchange due to the severe inflammatory
response. Constant CO levels were achieved, which is a
strength in this study compared to other studies, in which
the CO concentration decreased during the experiment
[8,11] or never was measured . The chosen target
concentration of CO (5% COHb) in the present study was
determined to be a clinically relevant dose, since higher
doses may induce toxic symptoms. A CO concentration of
20% in the blood may lead to unconsciousness [22,23].
Negative effects on performance during exercise after
carbon monoxide inhalation in healthy men can be seen at
CO levels from 4.8% COHb . Studies on patients with
angina pectoris show that carbon monoxide at levels from
2.7% to 4.5% COHb shortens the time to pain during
exercise and also induces a longer duration of pain
. Performance during exercise in patients with chronic
anaemia is reduced at 2.0% COHb . The relation
between CO dose and inflammatory response may be
important. Effects in pigs have been described at 1012%
COHb , but no effects in humans have been reported
at 7% COHb . If the previously suggested
anti-inflammatory effect of CO is found at these higher CO
concentrations, this may imply that the therapeutic potential of
CO is limited due to the risk of toxic side effects.
An important consideration regarding the animal model
is that the affinity of Hb for CO is dependent upon the
studied animal species. For example, mouse Hb has lower
affinity for CO compared with human Hb . Pig Hb has
lower affinity for CO than some other mammals, e.g. rat
and hamster . A lower affinity of Hb for CO could
result in a higher unbound or free fraction of CO, eliciting
a greater biological response at similar COHb fractions.
Elimination time for CO may also vary in different
species, as well as by differences in oxygenation. It has been
shown that the affinity of Hb for CO increases at low
oxygen tension . All of this has to be considered when
evaluating the proper dose of CO. This also points out
why it is of great importance to measure CO
concentrations in the studied subjects, in contrast to measurements
of ambient or inhaled CO levels.
In summary, no clear effects of CO on the systematic
inflammatory process were shown in this study conducted
in endotoxin administered pigs, as evaluated by measured
concentrations of plasma cytokines (TNF-alpha, IL-6,
IL1beta and IL-10). The model was characterised by massive
inflammation and a stable and controlled CO level. We
conclude that 5% COHb in the blood does not appear to
demonstrate any potential therapeutic effects on the
modulation of systemic inflammation in this porcine model.
The authors declare that they have no competing interests.
AM participated in the design of the study, the practical
work, the result discussion the statistical calculations and
writing the manuscript. PA participated in the practical
work, the result discussion and the revision of the
manuscript. GJ participated in the practical work, the statistical
calculations, the result discussion and the revision of the
manuscript. MH participated in the practical work, the
result discussion and helped to draft the manuscript. OW
participated in the design of the study, the result
discussion, revision of the manuscript and financial support. JEL
participated in the design of the study, the practical work,
the result discussion, the statistical calculations and in
writing the manuscript. All authors (AM, PA, GJ, MH,
OW and JEL) have read and approved the final
Financial support from the Medical Faculty, Ume University is gratefully
1. Motterlini R , Gonzales A , Foresti R , Clark JE , Green CJ , Winslow RM : Heme oxygenase-1-derived carbon monoxide contributes to the suppression of acute hypertensive responses in vivo . Circ Res 1998 , 83 ( 5 ): 568 - 577 .
2. Suematsu M , Goda N , Sano T , Kashiwagi S , Egawa T , Shinoda Y , Ishimura Y : Carbon monoxide: an endogenous modulator of sinusoidal tone in the perfused rat liver . J Clin Invest 1995 , 96 ( 5 ): 2431 - 2437 .
3. Nakao A , Kimizuka K , Stolz DB , Seda Neto J , Kaizu T , Choi AM , Uchiyama T , Zuckerbraun BS , Bauer AJ , Nalesnik MA , Otterbein LE , Geller DA , Murase N : Protective effect of carbon monoxide inhalation for cold-preserved small intestinal grafts . Surgery 2003 , 134 ( 2 ): 285 - 292 .
4. Otterbein LE , Otterbein SL , Ifedigbo E , Liu F , Morse DE , Fearns C , Ulevitch RJ , Knickelbein R , Flavell RA , Choi AM : MKK3 mitogenactivated protein kinase pathway mediates carbon monoxide-induced protection against oxidant-induced lung injury . Am J Pathol 2003 , 163 ( 6 ): 2555 - 2563 .
5. Otterbein LE , Bach FH , Alam J , Soares M , Tao Lu H , Wysk M , Davis RJ , Flavell RA , Choi AM : Carbon monoxide has anti-inflammatory effects involving the mitogen-activated protein kinase pathway . Nat Med 2000 , 6 ( 4 ): 422 - 428 .
6. Zuckerbraun BS , McCloskey CA , Gallo D , Liu F , Ifedigbo E , Otterbein LE , Billiar TR : Carbon monoxide prevents multiple organ injury in a model of hemorrhagic shock and resuscitation . Shock 2005 , 23 ( 6 ): 527 - 532 .
7. Hoetzel A , Dolinay T , Schmidt R , Choi AM , Ryter SW : Carbon monoxide in sepsis . Antioxid Redox Signal 2007 , 9 ( 11 ): 2013 - 2026 .
8. Mayr FB , Spiel A , Leitner J , Marsik C , Germann P , Ullrich R , Wagner O , Jilma B : Effects of carbon monoxide inhalation during experimental endotoxemia in humans . Am J Respir Crit Care Med 2005 , 171 ( 4 ): 354 - 360 .
9. Aberg AM , Hultin M , Abrahamsson P , Larsson JE : Circulatory effects and kinetics following acute administration of carbon monoxide in a porcine model . Life Sci 2004 , 75 ( 9 ): 1029 - 1039 .
10. Sundin AM , Larsson JE : Rapid and sensitive method for the analysis of carbon monoxide in blood using gas chromatography with flame ionisation detection . Journal of chromatography 2002 , 766 ( 1 ): 115 - 121 .
11. Mazzola S , Forni M , Albertini M , Bacci ML , Zannoni A , Gentilini F , Lavitrano M , Bach FH , Otterbein LE , Clement MG : Carbon monoxide pretreatment prevents respiratory derangement and ameliorates hyperacute endotoxic shock in pigs . Faseb J 2005 , 19 ( 14 ): 2045 - 2047 .
12. Tuchscherer M , Kanitz E , Puppe B , Tuchscherer A , Stabenow B : Effects of postnatal social isolation on hormonal and immune responses of pigs to an acute endotoxin challenge . Physiol Behav 2004 , 82 ( 2-3 ): 503 - 511 .
13. Brix-Christensen V , Gjedsted J , Andersen SK , Vestergaard C , Nielsen J , Rix T , Nyboe R , Andersen NT , Larsson A , Schmitz O , Tonnesen E : Inflammatory response during hyperglycemia and hyperinsulinemia in a porcine endotoxemic model: the contribution of essential organs . Acta Anaesthesiol Scand 2005 , 49 ( 7 ): 991 - 998 .
14. Myers MJ , Farrell DE , Palmer DC , Post LO : Inflammatory mediator production in swine following endotoxin challenge with or without co-administration of dexamethasone . Int Immunopharmacol 2003 , 3 ( 4 ): 571 - 579 .
15. Goldfarb RD , Dellinger RP , Parrillo JE : Porcine models of severe sepsis: emphasis on porcine peritonitis . Shock 2005 , 24 Suppl 1 : 75 - 81 .
16. Swindle MM , Smith AC , Hepburn BJ : Swine as models in experimental surgery . J Invest Surg 1988 , 1 ( 1 ): 65 - 79 .
17. Konrad D , Haney M , Johansson G , Wanecek M , Weitzberg E , Oldner A : Cardiac effects of endothelin receptor antagonism in endotoxemic pigs . American journal of physiology 2007 , 293 ( 2 ): H988 - 96 .
18. Frank JW , Carroll JA , Allee GL , Zannelli ME : The effects of thermal environment and spray-dried plasma on the acute-phase response of pigs challenged with lipopolysaccharide . J Anim Sci 2003 , 81 ( 5 ): 1166 - 1176 .
19. Bergmann M , Gornikiewicz A , Tamandl D , Exner R , Roth E , Fugger R , Gotzinger P , Sautner T : Continuous therapeutic epinephrine but not norepinephrine prolongs splanchnic IL-6 production in porcine endotoxic shock . Shock 2003 , 20 ( 6 ): 575 - 581 .
20. Javeshghani D , Magder S : Regional changes in constitutive nitric oxide synthase and the hemodynamic consequences of its inhibition in lipopolysaccharide-treated pigs . Shock 2001 , 16 ( 3 ): 232 - 238 .
21. Nalos M , Vassilev D , Pittner A , Asfar P , Bruckner UB , Schneider EM , Georgieff M , Radermacher P , Froeba G : Tin-mesoporphyrin for inhibition of heme oxygenase during long-term hyperdynamic porcine endotoxemia . Shock 2003 , 19 ( 6 ): 526 - 532 .
22. Kondo A , Saito Y , Seki A , Sugiura C , Maegaki Y , Nakayama Y , Yagi K , Ohno K : Delayed neuropsychiatric syndrome in a child following carbon monoxide poisoning . Brain Dev 2007 , 29 ( 3 ): 174 - 177 .
23. Mannaioni PF , Vannacci A , Masini E : Carbon monoxide: the bad and the good side of the coin, from neuronal death to antiinflammatory activity . Inflamm Res 2006 , 55 ( 7 ): 261 - 273 .
24. Ekblom B , Huot R : Response to submaximal and maximal exercise at different levels of carboxyhemoglobin . Acta Physiol Scand 1972 , 86 ( 4 ): 474 - 482 .
25. Anderson EW , Andelman RJ , Strauch JM , Fortuin NJ , Knelson JH : Effect of low-level carbon monoxide exposure on onset and duration of angina pectoris. A study in ten patients with ischemic heart disease . Ann Intern Med 1973 , 79 ( 1 ): 46 - 50 .
26. Aronow WS , Isbell MW : Carbon monoxide effect on exerciseinduced angina pectoris . Ann Intern Med 1973 , 79 ( 3 ): 392 - 395 .
27. Aronow WS , Stemmer EA , Isbell MW : Effect of carbon monoxide exposure on intermittent claudication . Circulation 1974 , 49 ( 3 ): 415 - 417 .
28. Aronow WS : Aggravation of angina pectoris by two percent carboxyhemoglobin . Am Heart J 1981 , 101 ( 2 ): 154 - 157 .
29. Klimisch HJ , Chevalier HJ , Harke HP , Dontenwill W : Uptake of carbon monoxide in blood of miniture pigs and other mammals . Toxicology 1975 , 3 ( 3 ): 301 - 310 .
30. Westphal M , Weber TP , Meyer J , von Kegler S , Van Aken H , Booke M : Affinity of carbon monoxide to hemoglobin increases at low oxygen fractions . Biochem Biophys Res Commun 2002 , 295 ( 4 ): 975 - 977 .